Xray's Test, Pre-Condition, Test Set, (Sub) Test Execution and Test Plan are all Jira issue types. That means that testing artifacts are also managed in the same way as any other issue type you may have (e.g. Bug, Story).

This is a core and unique characteristic of Xray that leverages the native features and brings them to your testing artifacts.

Let's see some characteristics related with Jira issues that you can take advantage of also for Xray issues.

Custom Fields

You may add additional custom fields to any Xray issue and include them in the screens.

Custom fields, whenever used properly, give the flexibility to provide additional information in a structured way to issues, so they can easily be accessed, searched and included in reports or even in Agile cards for example.

Who wins?

Jira admins Project admins

Workflows

You can implementation workflows also for testing related artifacts (e.g. Tests, Test Executions) to have full control over the lifecycle of the test specification or execution or planning phases.

With workflows you can even restrict that requirements are closed if they aren't properly tested.

Who wins?

Jira admins Project admins

Permissions

Deal with permissions as you deal with permissions in general for any issue in Jira. This simplifies and centralizes user and permission management.

Make your testing related issues read-only as you do for any other issue type.

Who wins?

Jira admins

Agile / Scrum Boards

Xray issues can be included in Scrum boards along with information from QA, thus everyone involved in the project can have a clear view about the real status of the issues being handled in the scope of some sprint, not just from a development perspective but also from a quality perspective.

Integration with other apps

Since JIRA issues is a core JIRA concept/artifact, they're used as the basis for many add-ons. Since Xray also uses JIRA issues, then the integration with many existing add-ons is available out-of-the-box, without having the needed of have a special integration for that to happen.

REST API

Reports / Listings

Xray issues can easily be included in listings since they're issues like every other one. Xray provides also some custom fields for each issue type that can be used in order to provide some relevant information, in the context of the entity that is being shown (e.g. "requirement status" for showing the coverage status of a requirement, or the "Test Execution Status" for showing the progress of a Test Execution).

The "Filter Results" gadget can also list Xray issues in order to make listings of Tests, Test Sets, Tests Plan or requirements and include, for example, information about their status.